1. Field of Invention
This invention relates to the determination of the degree of unbalance and the balancing of a rotating assembly such that the vibratory effect of having the center of rotating mass eccentric to the axis of rotation is minimized.
2. Related Art
It is necessary that the center of mass of rotating assembles are concentric with the axis of rotation for optimal performance of their respective functions. Any deviation from this concentricity will represent additional forces which must be borne by a given structure that supports the rotating assembly. These additional forces manifest themselves as vibration and can not only interfere or diminish the ability of the rotating object to perform its function but can also accelerate the fatigue life of all the interconnected components themselves e.g. bearings, gears, shafts, structural supports connected to the rotating assembly. In wind turbines, the increase in the degree of unbalance not only decreases the mechanical life of connected components but will also increase the necessary wind velocity required for the generation of power.
It is well known in the art to balance a rotating mass as a complete assembly. The art is generally limited to rotating masses which are sufficiently small in diameter, have sufficient speed, and can be measured without external forces such as those which are environmentally induced. Additionally, prior art relies on a vibratory response of the unbalance which could be either diminished or amplified by the supporting structure of the rotating assembly. Furthermore, in order for a corrective balance solution to be determined, prior art requires that a vibratory response is first known and then knowing the vibratory response of a known mass placed at a known location before a corrective balance solution is determined. The balancing solution becomes prescriptive only after the series of trial runs are performed. These vibratory responses are measured with displacement, velocity, or acceleration transducers, each with their respective limitations relative to machine configuration and machine angular velocity. Vibratory response will be exponentially proportional to product of the mass unbalance and the square of angular velocity. Low speed applications require specialized equipment to assess vibratory response, especially below 60 RPM where specialize instrumentation is required due to the decreased signal-to-noise ratio.
U.S. Pat. No. 5,140,856 to Larson (1992) teaches one method of a balancing a complete assembly whose parameters fall outside of the well known art which requires the use of fixtures, specialized equipment and associated skill set, and personnel to perform the process at great heights and in proximity to rotating equipment. The method is time consuming and also extremely subject to environmental influences such as wind which will thereby affect the accuracy of the results. This method relies on not only upon the vibratory response of the unbalance upon the structure but requires the installation of a known mass at a known location to determine the location and magnitude of the unbalanced force prior to the determination of a corrective balance solution.
It is desirable to have a novel method and apparatus to determine the degree of unbalance on a rotating assembly which has a non-vertical axis of rotation that provides a simple, practical, prescriptive, and economical means to assess the severity of the condition and is independent of the structure's vibratory response to the unbalance. Additionally, any improvement in reducing the risk to personnel, minimizing the level of skill, reducing the time required for correction, as well as being able to provide a means to quickly assess the severity of a population of assets in this class is highly desirable. It is also desirable to have a method to provide for a corrective balance solution which is not influenced by the supporting structure and is prescriptive without the need for a trial and discovery process.